1. Field of the Invention
The present invention relates to an X-ray diagnostic apparatus or a radiographic apparatus having a function for removing scattered X-rays.
2. Description of the Related Art
When radiography is to be performed in a radiographic apparatus, X-rays are radiated from an X-ray source onto an object to be examined at a relatively large dose, and the X-rays transmitted through the object are recorded on an X-ray recording medium (an X-ray film cassette) arranged within the X-ray radiation range. In this radiographing method, however, the X-rays are scattered by the object, and a radiographic image includes a large amount of scattered X-rays from the object, resulting in degradation of the image quality of the radiographic image.
For this reason, the following radiographic apparatus has been developed. In this apparatus, in order to obtain one radiographic image, X-rays are radiated on a subject while they are formed into a slit-like beam by a slit, or X-rays which are transmitted through the subject upon radiation are formed into a slit-like beam by a slit, and the slit is moved.
According to another system, X-rays are formed into a slit-like beam, and are radiated along a subject. X-rays which are transmitted through the subject are converted into an electrical signal by a line sensor. While slit-like radiographic data is obtained in this manner, the slit-like X-ray beam and the sensor position are synchronized with each other, thus obtaining one radiographic image.
In a radiographing operation using one slit member as described above, scattered X-rays from a subject cannot be effectively removed. For example, when X-rays are radiated on a subject after they are narrowed down by a slit, since the X-rays are scattered in the subject, the X-rays transmitted through the subject have an inverted U-shaped distribution and spread in a wide range. When X-rays are narrowed down by a slit after they are radiated on the subject, the X-rays transmitted through the slit have a narrower distribution than the former case. However, since scattered X-rays from the subject pass through the slit, the amount of scattered X-rays becomes large as in the former case. In addition, since X-rays are radiated on the entire subject in a radiographing time, the dose of X-ray radiation on the subject is increased.
Furthermore, since a line sensor is constituted by a CCD sensor having a fluorescent material in its light-receiving surface, it is inferior to a film in terms of technical limitations on the sensor length, pixel variations, dynamic range, and the like. In addition, the conventional radiographic apparatus is complicated in electronic arrangement. Moreover, the resolution is degraded upon movement of a subject due to limitations on the operation speed of an electronic circuit.